How do you measure the success of a major implementation project?

ROI
Client satisfaction

Productivity (project costs deviations in time, money and resources)
Team and company experience (lessons learned)

The measure of a successful project is how satisfied the end-users are with the result. There's going to be bumps in any technology project. Things aren't always going to go perfect. Software is imperfect by nature. You can plan as much as you can but you're always going to hit some snags during deployment week. But ultimately the end-users are either satisfied or they're not satisfied, regardless of those blips.  So the way that I measure my personal effectiveness is related to that. "Has this made your day-to-day lives easier?" That's super important, because technology is an enabler; it is not the one doing the job for you. The people are doing the job; the tools are what are enabling them to do that. So if they're not doing that and they're actually doing the opposite, then that's not success for me. Number two is, the folks who worked on the project, what was their experience like? Did they feel successful? Does the team feel like they delivered a good product or service? And if not, why? That's also a critical area that I measure myself on. So those are the two core things I look at in a project post-mortem perspective.